Arrange a cooking wrack atop a baking sheet.
Add a minimum of 4 inches of vegetable oil to a large heavy-bottomed stock pot set over medium-high heat. Attach a deep-fry thermometer to the side.
Once the oil reaches 300°F, add a portion of the potatoes and cook, stirring occasionally, until the potatoes are pale golden, about 2 minutes. Using a sieve or slotted spoon, transfer the potatoes to the baking sheet then repeat the frying process with the remaining potatoes, returning the oil to 300°F between batches. Do not overcrowd the pan.
Once the potatoes have cooled, fry them a second time at 360°F until golden brown and crispy, about 2 minutes. Using a slotted spoon, transfer them to a bowl, season with salt or other spices and toss to combine. Serve immediately.